Iridium(III) Blue Phosphors with Heteroleptic Carbene Cyclometalates: Isomerization, Emission Tuning, and OLED Fabrications

Abstract Ir(III) complexes are particularly noted for their excellent photophysical properties in giving blue OLED phosphors. In this study, two distinctive carbene pro‐chelates LAH 2 + and LBH 2 + (or LCH 2 + ) were employed in preparation of heteroleptic Ir(III) complexes, to which LAH 2 + bears a cyano substituted benzoimidazolium along with N‐mesityl appendage, while LBH 2 + (or LCH 2 + ) carries the symmetrical benzoimidazolium entity. Notably, the reversible equilibration at high temperature was observed for m , f ‐ ct14 and m , f ‐ ct15 with a single LA chelate. In contrast, only the mer ‐substituted m ‐ ct16 was obtained upon employing two LA chelates. All Ir(III) complexes exhibited blue photoluminescence ( Φ PL 78 %) with short radiative lifetimes (τ rad 1.05 μs) in solution. The Ph OLED device with m ‐ ct16 afforded an external quantum efficiency (EQE) of 22.8 % at 5000 cd ⋅ m −2 . Moreover, the hyper‐OLED based on m ‐ ct16 and v‐DABNA exhibited EQE 1000 of 32.1 % (EQE recorded at 1000 cd ⋅ m −2 ) and J 90 of 15.0 mA cm −2 (current density at 90 % of max. EQE). Its suppressed efficiency roll‐off (EQE of 32.1 % and 27.7 % at 1000 cd ⋅ m −2 and 10000 cd ⋅ m −2 ) demonstrated a milestone in fabrication of blue OLED devices.